An astronomical telescope, which is a representative of optical devices, having an object lens fixed at a front end of a cylindrical section and an eyepiece, which are provided on a straight line, is popularly used.
To observe celestrial bodies with such a telescope, first the cylindrical section should be set in parallel to the earth's axis, and then the telescope is directed to the object star by setting an equatorial mount of the telescope to the object star's declination and codeclination.
During this operation, the position of the eyepiece, when the telescope is set in parallel to the earth's axis is, different from the position thereof when the telescope catches the object star, therefore it is quite inconvenient for a physically handicapped person on a wheelchair.
When a camera is attached to the eyepiece to take a photograph, a long time exposure is sometimes required.
In this case, the whole of the telescope should be rotate on an axis parallel to the earth's axis in the sidereal time, and the position of the eyepiece of the starting rotation is different from the position of the finishing rotation.
A coude telescope whose eyepiece can be positioned at a fixed position is shown in FIG. 11.
The cylindrical section of the telescope shown in FIG. 11 is bent midway at a right angle and reflectors 38 and 38 are provided at the corners of the bent section.
Incident light into the front end of the cylindrical section 12 passes through an object lens (not shown) and is reflected on the reflectors 38 and 38 toward an eyepiece 26.
In this telescope, an axis X--X of a cylindrical section 12' can be kept in parallel to the earth's axis when the object lens is directed to an object star.
Further, the telescope can trace the object fixed star by rotating the cylindrical section 12' on the axis X--X parallel to the earth's axis in the sidereal time.
Because of keeping the axis X--X of the cylindrical section 12' parallel to the earth's axis, the position of the eyepiece can be fixed at one position.
In the telescope shown in FIG. 11, however, the incident light is reflected in the midway between the object lens and the eyepiece 26, so that an optical path therebetween is long and the structure is not improper for a telescope having a light visual range with large diameter and short focal length. Therefore, it is improper to observe dark fixed stars, nubulas, etc.
In a reflecting telescope shown in FIG. 12, a light reflected and focused on reflectors 41 and 42 is reflected on a reflector 43 to focus into an image at point F which is in front of an eyepiece 47. In this reflecting telescope, a cylindrical section thereof can be rotated on an axis Z--Z by a gear 45 to adjust declination, and, at the same time, the cylindrical section can be rotated on an axis Y--Y by a gear 44 to adjust codeclination during observation.
In this reflecting telescope, however, position of an eyepiece 47 is rotated on the axis Y--Y.
Further, an observation room in which the telescope is accommodated is required, and there must be provided a window, which can be opened and closed, in the ceiling section thereof.
Therefore, the cost for installing the telescope should be quite high.
The inventor of the present invention proposed a telescope, which solves the disadvantages of above described telescopes, which can shortened the optical path between an object lens and an eyepiece and which can keep a position of the eyepiece at one position while tracing fixed stars, in a specification of Japanese Patent Application No. 62-148656.
This telescope has, as shown in FIG. 13, a reflector 30 at a front end of a cylindrical section 12, and the cylindrical section 12 can be rotated by a driving means 13.
In this telescope, the reflector 30 reflects a light, which comes in the direction of a finder 20, in the direction parallel to an optical axis of an object lens (not shown) provided at the front end of the cylindrical section 12.
With this structure, an object star can be caught in a visual range without adjusting position of an eyepiece 26 by directing the finder 20 toward the object fixed star after setting the cylindrical section 12 to be parallel to the earth's axis, and a telescope having large diameter and short focal length can be provided.
Further, the telescope can trace the object star by rotating the cylindrical section 12 in the sidereal time keeping parallel to the earth's axis.
In the telescope shown in FIG. 13, the observable range is limited because of single reflector 30. To observe the unobservable range, a secondary reflector should be attached to the reflector 30.
The secondary reflector is fixed, so that the range, which can be observed without the secondary reflector, cannot be observed when the secondary reflector is attached.
Therefore, the secondary reflector sometimes should be attached or detached when the object star is changed.
Further, the direction of the secondary reflector does not coincide with the direction of the finder 20, so that it is necessary to direct the secondary reflector toward an object star considering the direction of the finder 20 (or the direction of the reflector 30).
Then object of the present invention is to provide an optical device, which can easily observe an object bodies positioned in any direction while keeping the position of the eyepiece at one position, and which can preferably shortened an optical path between an object lens and an eyepiece to get a light visual range.